The invention relates to an automatic exposure controller for a camera, and more particularly, to such controller in which a digital processing technique is employed to perform an arithmetic operation to determine an exposure period.
The recent trend is to use a digital circuit to form an automatic exposure controller for a camera. This is because in the data processing relating to exposure information, the use of digital signals affords a greater flexibility, and avoids the occurrence of leakage currents or a change of stored data with time, which is experienced in dealing with analog signals. Thus digital processing is more suitable for use in the exposure controller of a camera. On the other hand, an analog circuit can be simplified in its circuit arrangement as compared with a corresponding digital circuit. Also, where a digital circuit is used, there is a problem related with an error which is caused by the quantization of analog quantities which is required in using a digital circuit. For this reason, an analog circuit may be suitably used where the circuit arrangement requires increased accuracy. In an automatic exposure controller for a camera, an analog voltage proportional to the logarithm of the brightness of an object being photographed is converted into a digital format, and an exposure period is determined through a given arithmetic operation. A variety of techniques are available for expanding the digital version of the exposure period into a real time, but involve a complex circuit arrangement, an unsatisfactory accuracy or a complex calculation.